Improved numerical methods for gammatone filterbank analysis and synthesis

The article "Frequency analysis and synthesis using a gammatone filterbank" [1] introduces an efficient implementation of all-pole gammatone filters with complex-valued output. It describes the design of an auditory filterbank using these gammatone filters, together with a low-delay synthesis method. This article introduces an improved numerical method for deducing the phase factors necessary for the synthesis part of the analysis-synthesis system. This method gives more accurate results compared to the original proposal in some cases. Also introduced is a numerical optimization procedure to deduce band-specific weight factors needed for the synthesis stage. Finally, a method is introduced to reduce the computational cost of the already efficient gammatone filter implementation by approximately 60%, at the cost of storing additional tables of precomputed parameters.